a. Field of the Invention
This invention relates to 2'-(4,6-disubstituted-s-triazin-2-yl)amino-9'-dialkylamino[1'a,4'a]benzofl uorans useful as color precursors, particularly in the art of carbonless duplicating systems as, for example, pressure sensitive and thermal systems and to processes for preparing said 2'-triazinyl-amino-substituted-9'-dialkylamino[1'a,4'a]benzofluorans.
B. Description of the Prior Art
Several classes or organic compounds of widely diverse structural types are known to be useful as colorless precursors for carbonless duplicating systems. Among the more important classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides, for example, crystal violet lactone; fluorans, for example, 2'-anilino-6'-diethylaminofluoran and 2'-dibenzylamino-6'-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Moriga and Oda (Univ. Kyoto, Japan) in Kogyo Kagaku Zasshi 67 (7), 1054-8 (1964) [Chemical Abstracts 62: 2852a (1965)] describe the preparation and properties of a 3,3-bis(4-dimethylaminophenyl)phthalide which is substituted in the benzene ring of the phthalide moiety by a 4,6-dichloro-s-triazin-2-ylamino group. The compound is described as producing a green image when developed on bentonite in a simulated carbonless duplicating application. However, this prior art compound exhibits a number of deficiencies when employed in such a system which render it generallly unsuitable for application in commercially feasible copy systems in light of the industry's standards for colorless precursors. Thus, its rate of color formation, upon contact with an electron withdrawing media such as an acidic clay or phenolic resin has been found to be rather slow. The intensity of tinctorial strength of the developed color produced by the reference compound has been found to be less than that generally found economically acceptable in the art when used within the concentrations usually employed in carbonless copy systems. Further, the solubility of the prior art compound in solvents regularly used in the copy system art for dissolving the dyes for microencapsulation is below that generally required to provide sufficient concentration of the dye to obtain satisfactory tinctorial strength in the developed form. Possibly the most important deficiency of the phthalide of Moriga and Oda is the low susceptibility to copiability of their color-developed form in standard copying machines, for example, a Xerox copier. By contrast, the compounds of this invention have been found to overcome the deficiencies of the prior art compound in that they proved to have a rapid rate of color formation on contact with acidic developing media; they have a good to excellent tinctorial strength to weight ratio; they are satisfactorily soluble in the usual microencapsulating solvents; and their developed color form is highly copiable in duplicating machines.